With a power-driven hand-held cutting device, an operator may e.g. cut or saw vegetation, such as trees, bushes, branches, grass, etc. Many power-driven hand-held cutting devices today are equipped with some sort of brake assembly. Such brake assembly may include a hand guard arranged to activate a brake. When such assembly is used in the technical field of chainsaws, the assembly may be referred to as kick back safety assembly, chain brake assembly, or kick back guard. Such assembly is arranged to hinder rotation of a rotatable part of a transmission of the chain saw to thereby hinder the movement of the chain if the guide bar of the chainsaw is kicked towards a user. Since the assembly is intended to protect a user from being injured by a moving chain, there are various requirements on such assembly. For instance, when the hand guard reaches a position in which the brake is intended to be activated, the brake must be activated with high reliability. Further, the brake must stop the chain as soon as possible in order to avoid injury of the user.
Attempts have been made to provide a brake assembly for a power driven cutting apparatus, for example a brake assembly for a chainsaw as described in the document U.S. Pat. No. 3,664,390 A. The saw described in this document has a hand guard arranged between a handle of the chainsaw and the guide bar. In case the chainsaw kicks back, the hand guard is pushed to a position, usually by the upper side of a user's hand, in which position the brake assembly is activated. The brake assembly is associated with a number of drawbacks. For example, after the brake has been activated, the brake may unintentionally be inactivated.
A conventional kick back brake for a chainsaw uses a brake band wound around a brake drum, which brake drum is fixedly connected to a drive sprocket for driving a cutting chain. Upon kick back a hand guard is pivoted and thereby arranged to activate the kick back brake. By activation of the brake one end of the brake band is pulled and thus tightened around the brake drum so that the drum and thus the chain stops.